1. Field of the present invention
This invention relates to a projector for projecting a image or object on a plate-like transparent material such as a photographic slide, a prepared specimen for microscopic observation file sheet onto a screen, specifically to a projector for a file sheet having a plurality of matrix-like arranged such transparent materials to be projected.
1. Description of the prior art
Japanese Patent Publication No. 55-47731 discloses a file sheet for a photographic slide or a prepared specimen in which a plurality of transparent materials are arranged in row and column respectively so that the transparent materials can be projected and observed as they are held on the file sheet. The file sheet can be conveniently bound in an album and the like as it is for facilitating a pigeonholing.
The Japanese Patent Publication illustrates that the transparent material is projected by a projector on a screen as it is carried by the file sheet. Japanese Utility model application 58-10421 laid open to the public in 1983 and Japanese Patent Publication 58-21247 published in 1983 disclose similar projectors thereto. The projector comprises a housing on which a support frame is disposed for carrying a file sheet. The support frame is provided with a carrying surface for carrying the file sheet thereon. The carrying surface is formed with a hole through which an image or information on the transparent material is projected. The file sheet is positioned on the carrying surface of the support frame resulting in positioning the transparent material. Thereafter, the projector is subjected to an focus adjustment with an optical system thereof.
As a matter of fact, it should however be noted that the file sheet is difficult to be kept in a perfect plane condition when positioned. This means that the file sheet partially comes up to produce a partial offset from the carrying surface thereon when it is carried on the carrying surface. The partial offset of the file sheet affects the focusing condition of the optical system. Consequently, even after a focusing work is done with regard to a transparent material on a file sheet, a further focus adjustment may be necessitated for another transparent material on the same file sheet because of possible different distance to the carrying surface from each transparent material in the case where the other transparent material on the file sheet is being prepared for projection. The partial offset is caused by various factors.
For example, the support frame is movably mounted on the housing in only a longitudinal direction wherein the file sheet is slid in a transverse direction to select a transparent material for projection in a relatively simple projector. Where the transparent material for selection is located at one end portion of the file sheet, the other end portion of the file sheet is extended over the support frame to hang down. This causes the partial offset around a transparent material positioned for projection.
There has been known a projector provided with a click stop roller for being engaged with a cut out portion formed on a file sheet in order to position the file sheet with regard to the transverse direction. In this type of projector, the click stop roller urges the file sheet from the opposite side thereof in the longitudinal direction so that the partial offset occurs in intermediate portion of the file sheet.
In order to prevent such partial offset, Japanese Utility Model Publication No. 58-29455 published in 1983 proposes a projector provided with a retaining device for retaining a subject on the carrying surface. The retaining device is provided with a retaining frame movably mounted on an outer cylinder of an optical projecting mechanism of the projector wherein the retaining frame is urged downwardly by means of a spring to retain a file sheet around a transparent material positioned for projection onto a carrying surface of a carrying frame. In this conventional retaining device, it is necessary to lift the retaining frame up against a resilient force of the spring so as to keep the frame away from the carrying surface for allowing the file sheet to be moved longitudinally and/or transversely in each time when a transparent material is replaced for projection. This makes an operation of the projector complicated.